The present invention resides in a differential transmission in bevel gear configuration including at least one planetary gear and opposite center gears, which are in engagement with the planetary gear, that is, rotatably supported about an axis normal to the axis of the center gears in a transmission casing, which encloses the center gears and the planetary gear and is rotatable about the axis of the center gears.
In a known differential transmission in bevel gear configuration as disclosed in DE 195 36 800 A1, the one-piece transmission casing includes bearing necks which extend co-axially with the central axis of the transmission. They are displaced in the direction of the central axis with respect to the adjacent center gear toward the adjacent center gear and supported by a tapered roller bearing on the stationary outer housing. The central opening of the respective bearing neck has an inner diameter, which is only slightly larger than the inner diameter of the adjacent center gear so that this center gear can be axially supported on an inner axial bearing surface of the transmission casing in the direction of the central axis from the axis of rotation of the planetary gear toward the bearing neck. In the central opening of the respective bearing neck, the end portion of the drive shaft, which is rotationally fixed to the adjacent center gear, is rotatably supported by a radial friction bearing. The extension of the mounting opening in the outer housing for the installation of the differential gearing is in the direction of the bearing axis essentially as large as the distance between the axial front faces of the bearing necks as measured in the direction of the central axis so that the rigidity of the outer housing is limited. Furthermore, the bearings of the outer housing must be divided along a housing plane, which includes the bearing axis in order to permit insertion of the differential transmission into the outer housing without substantial tilting. This bearing division further reduces the housing rigidity. Also, the manufacture of the transmission housing is expensive because the inner support and bearing surfaces cannot be formed by drilling but only with the aid of special cutting tools.
It is the object of the present invention to provide a differential transmission, which is relatively simple and easy to assemble, and a method of assembling the transmission.
In a differential transmission including a differential transmission casing with planetary bevel gears supported therein so as to be rotatable about an axis normal to a center axis of the transmission casing, and two center gears arranged at opposite sides of, and in meshing engagement with, the planetary bevel gears, the differential transmission casing has at least at one end thereof a cylindrical casing extension having an opening which is concentric with the center axis and into which an insert is fitted which has an outer end projecting from the casing extension and forming an annular bearing section for rotatably supporting the differential transmission casing in an outer transmission housing.
With the differential transmission according to the invention, the transmission casing can be manufactured by drilling because of the large openings for the housing inserts. With the method according to the invention, the differential transmission can be installed in the outer housing with ideal parallel orientation of its central axis to the bearing axis of the outer housing by way of the assembly opening of the outer housing without the need for divided bearings.
In the differential transmission according to the invention, the length of the mounting opening in the outer housing in the direction of the bearing axis can be reduced by the respective bearing length that is by the respective length of the bearing section at both housing inserts so that the lengths of transmission casing and of the outer housing are correspondingly reduced. Also, the arrangement is more rigid and the weight of the transmission is reduced.
With the machining of the transmission housing by drilling the establishment of the axial distance between the center gears and the axis of the rotation of the planetary gears is simplified and more accurate.
Each center gear can be axially supported by an axial bearing surface of the transmission casing. The respective center gears can be inserted in a simple manner into the transmission casing by way of the opening accommodating the respective housing extension if the diameter is selected so as to be larger than that of the adjacent center gear. There are no restraints cornering the bearing type and configuration of the bearing section of the housing insert. This may be, as is conventional, a complete anti-friction bearing arrangement for example with a separate inner race ring for supporting the bearing rollers.
The inner race of the bearing may also be provided on the bearing section of the housing insert wherein a coating of a special bearing material may be provided on the housing insert to form the race for the rollers or balls.
With the arrangement according to the invention, the bearing section or, respectively, the whole housing insert may consist of a bearing material so that the inner bearing race can be an integral part of the insert.
The distance of the housing insert from the axes of rotation of the planetary gear may be determined advantageously by a radial projection of the differential casing forming a stop.
Each center gear may abut an axial bearing surface of the respective adjacent housing insert, which is particularly advantageous if the housing insert consists of a hard material. Bearing washers may be eliminated thereby.
The transmission casing may consist of a single part even if four planetary gears are disposed between the center gears. Four planetary gears are often used in differential transmission for commercial vehicles. Even in this case all the planetary gears can be inserted into the casing by way of the openings provided for the extensions of the housing inserts.
The axle shaft, one end of which is mounted on one of the center gears for rotation therewith extends to a vehicle wheel which may be radially supported in the housing insert that is disposed adjacent the respective center gear. In this way, no outside axial forces become effective on the center gear.
The outer transmission housing may include a radial mounting opening for the installation and the support of the transmission casing without the need for providing divided bearings for the outer transmission housing.
For the installation of the transmission casing into the outer housing, the respective installation opening of the outer housing can be narrower in the direction of the bearing axis by at least twice the length of a tapered roller bearing in comparison with a conventional differential transmission, without any deviation from the advantageous parallel orientation of the center axis of the differential transmission with regard to the bearing axis of the outer housing during insertion of the differential transmission through the installation opening.
A particular embodiment of the invention will be described below on the basis of the accompanying drawings.